You might have an STI you aren't aware of.

Undiagnosed STIs can lead to inflammation of the cervix and bleeding.
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Bleeding after sex could be an indication of an undiagnosed STD. "The inflammation of your cervix causes the blood vessels there to swell," Ian Currie, consultant gynecologist at BMI The Chiltern Hospital told Women's Health. As you continue to have sex, the blood vessels have a greater potential to burst.

One type of STI is trichomoniasis which is caused by a single-celled parasite. Cervical discharge and bleeding are the most common symptoms of trichomoniasis. Fortunately, it is easily treated with an antibiotic, Very Well Health reports.

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When your vagina is dry, bleeding can occur.

Causes such as menopause can lead to a dry vagina. When your vagina is dry, you may experience bleeding from friction during sex, the NHS reports. This can be helped by talking to your doctor about what could be causing vaginal dryness, using proper lubrication, and starting slow.

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Polyps aren't dangerous, but they may cause bleeding.

Polyps can irritate surrounding areas which can lead to bleeding.
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Endometriosis is a common cause of bleeding post-sex.

Bleeding after sex is one of the symptoms of endometriosis.
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The under-discussed condition of endometriosis occurs when the tissues that line the uterus, grow outside the uterus. Endometriosis can cause extreme pelvic pain, heavy periods and bleeding after sex, Medical News Today reports. If you have other symptoms of endometriosis, including bleeding after sex, you should talk to your doctor.

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You have one of a myriad of infections.

Beyond STIs, there are a variety of infections that could lead to bleeding during sex. According to Women's Health, one of the most common infections is pelvic inflammatory disease. "PID is an infection of the gynecological organs and affects the womb, ovaries and Fallopian tubes," London-based consultant gynecologist Tania Adib told Women's Health. It generally occurs due to mild bacteria and can be treated with antibiotics.

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Postmenopausal people have a higher chance of bleeding after sex.

Less estrogen can create less lubrication and a thinner barrier.
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Experiencing breakthrough bleeding can coincide with sex.

Mid-cycle bleeding can happen on oral contraceptives.
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Breakthrough bleeding, also known as mid-cycle bleeding, can happen to women taking an oral contraceptive. "Some women experience breakthrough bleeding while they are on the pill and coincidentally this can happen while they are having sex," Currie told Women's Health "The intercourse itself is not causing the bleed but the motion may prompt it to happen."

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Vigorous sex can lead to an increased chance of bleeding.

Intense sex can lead to cuts and tears.
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When you have more intense sex, the odds of cuts and tears on the vagina increase. Very Well Health reports that when these cuts happen, you're more likely to bleed during sex. Taking it slow and using plenty of lubrication can lessen these odds.